Method for rehabilitating scored and marred surfaces

ABSTRACT

Metal, carbon, or other original surfaces of articles, such as pneumatic and hydraulic cylinders, having scored or marred surfaces can be rehabilitated by applying to them a composition consisting essentially of a mixture of powdered molybdenum disulfide and epoxy resin, curing the resin, and removing excess material. The coating is as hard as steel, has lubricative action, and can withstand high temperatures.

This is a division of application Ser. No. 279,889, filed Aug. 11, 1972.

BACKGROUND OF THE INVENTION

This invention relates to a lubricative coating and filling compositionfor use in restoring metal surfaces that have been scratched, scored orgrooved. It also relates to a method of restoring damaged surfaces.

Heretofore, when metal surfaces were damaged in such apparatus aspneumatic and hydraulic cylinders, they have been difficult to repair,and the repair has been expensive. The usual prior-art process offilling scores and grooves in cylinders and hot castings comprisedfirst, grinding off the damaged surface to the depth of the deepestscores or grooves, then plating the ground-off surface with chromium ornickel, and then regrinding and repolishing the plated surface. Each ofthese steps was expensive and time-consuming, and the deeper the damage,the more difficult and expensive and lengthy became the repair process.

Siimilar problems were met with bearing journals and bell housings wheresurfaces had to be built up, and the prior-art practices were equallyunsatisfactory there, too.

Attempts have been made to restore such damaged surfaces by using epoxycements, but the results were unsatisfactory, for they either lacked thenecessary lubricative quality or were applicable only in very thinlayers -- up to a maximum of only about 0.0005 inch.

Objects of the present invention are to provide a more satisfactory andless expensive way of repairing such damaged surfaces and to provide animproved composition and improved method for doing this.

SUMMARY OF THE INVENTION

The composition of the invention consists essentially of a mixture of anepoxy resin and molybdenum disulfide in powdered form. Variousproportions can be used in the range of 90% of either ingredient to 10%of the other ingredient, the best results usually being obtained whereapproximately equal volumes of the two ingredients are used, or a rangefrom 40% epoxy resin and 60% molybdenum disulfide to 60% epoxy resin and40% molybdenum disulfide these percentages being by volume.

The mixture may be wiped on to the metal surface, or the mixture may bethinned with a suitable volatile solvent and then sprayed on to themetal surface. After the surface has been coated (either by spraying orby wiping on the mixture) such surface is wiped to remove any excessmixture where it extends significantly above the surface level. Thesolvent, if any, is evaporated. Where the mixture has been sprayed on,the solvent is evaporated prior to wiping. Then the epoxy resin is curedat an elevated temperature. Finally, the surface may be finished bygrinding and polishing.

After cure, the material has a Rockwell hardness of mild steel and hasalso remarkable properties of withstanding high temperatures andconsiderable mechanical forces. In addition, it provides a lubricatingaction. Furthermore, it can fill deeper scores and build up greaterthicknesses than could prior-art processes.

In addition to replacing the grind-plate-grind process on repairs tosleeving and other expensive repairs for cylinders, shafts, bushings,bearings, and other metal surfaces, the material of this invention isused to fill damaged areas caused by scoring, by scratches, by weargrooves in sealing rings or springs, by fretting, by galling, bycorrosion pitting, and so on. It can also be used to renew the sealingsurfaces on carbon, Teflon, and metal sealing rings and packing. It canbe used to fill various types of voids. It renews and builds upoversized or pitted bearing bores in bell housings, bodies, and so on.It can be used to fill and seal cracks in housings and bodies. It can beused to seal and protect armature and stator windings from oil and otherdamage.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a graph showing tensile shear strengths at varioustemperatures for two different base compositions used in combinationwith a material embodying the principles of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Powdered molybdenum disulfide of various kinds can be used. One suitableproduct is "Molykote 2" dry lubricant, a Dow-Corning product, but othermolybdenum disulfides are usable. The powder should be fine, preferablywith particle sizes no larger than 60 microns diameter.

The epoxy resin, which is a glycidyl polyether of bisphenol A,preferably containing suitable curing agents, such as certain amines,may be chosen from a variety of available materials, with one of themost satisfactory being the proprietary product known as Epon Adhesive929 manufactured by Shell Chemical Corporation; this is also known asAerospace Adhesive EA-929, as Hysol Adhesive EA-929 and as ADH 3002-17made by the Hysol Division of the Dexter Corporation. This material isdiglycidyl ether of bisphenol-A and is a fast curing, one pan,yellow-green thixotropic paste with a typical viscosity of 400,000 cpsat 75° F. using a Brookfield HBT No. 7 spindle at 20 RPM. The materialcan contain a small amount of triphenylmethyl phosphonium iodide; and ithas a density of 1.4 and a shelf life of several months at up to 75° F.As curing agent there can be used, suitably in admixture with the resinas starting material herein, an amine or hydroxyl curing agent therefor,such agents being well known in this art, both as to kind and amountused. A very satisfactory resin of the type described herein for use asthe adhesive agent is a diglycidyl ether of bisphenol-A containing anamine curing agent, the mixture being stable at room temperature butcuring quickly upon heating. The recommended cures are for 3 to 4 hoursat 250° F, 40 to 80 minutes at 300° F., and 10 to 40 minutes at 400° F.For prolonged storage, the material is preferably kept below 90° F. andeven better, below 75° F.

The two materials, the epoxy resin and the molybdenum disulfide powder,may be mixed together in practically any porportions with results thatvary somewhat. The results are usually best when the two materials areapproximately in equal volumes, but they may be used with as high as 90%by volume epoxy to 10% by volume molybdenum disulfide or with 90% byvolume molybdenum disulfide and 10% by volume epoxy resin. For mostapplications, the preferred range is within 40 to 60% by volume of eachingredient with the balance being the other ingredient.

The material may be wiped on in the viscous paste form but it may alsobe applied by spray, if desired, by first thinning it with a suitablevolatile solvent. Any suitable volatile solvent may be used, but onedesired such solvent is known as PT-1001, which is methyl ethylenechloride. Three parts of the thinner to one part paste gives a suitableviscosity for spraying.

The material, especially in paste form, can be built up to any thicknessdesired and even in spray form it can be built up by correct applicationtechnique. It can be built up to a great thickness and may be locallyapplied instead of applying it over the entire surface of the damagedpart. When applied, the material is used to fill all the grooves,scores, and other mars and may, if desired, be wiped off to remove someexcess. Then it is cured at the recommended curing temperatures for theepoxy resin, by heating until cure is completed, and the heating may bein an oven or by infrared or by heat applied to the surface in anydesired way. After cure, the material may be ground or polished or bothto remove any excess remaining. Often, and especially when it has beenapplied by spraying, no grinding is needed, and even polishing may oftenbe dispensed with.

The cured material has a self-lubricating quality, maintains itsadherence under great pressure and temperature, for example 16 tons persquare inch, and up to temperatures over 600° F. The material does notsoften or dissolve when exposed to hydraulic fluids, including Skydrol,or oils or greases, and it has shown resistance to cleaning solvents,such as Freon, Stoddard's solvent, kerosene, and gasoline. It can beused to build up metal surfaces, as in bearing journals and bellhousings and can be applied in many places where plating heretofore hasbeen required, usually saving the grinding and machining process usedprior to plating. It can be applied on materials that are not amenableto plating, and the application can be extremely simple and quick, withthe setting time brief, depending upon the temperature used.

For best results, a damaged metal surface is prepared before applyingthe material of this invention by first stripping any protective paintor covering, if there is any. Then the surface is wiped with a suitablesolvent to remove greases and dirt, continuing to clean until a solventmoistened cloth shows no residue; vapor degreasing can be used instead.All areas to be filled with the material of this invention should beabraded and cleaned. Grit or vapor blasting can be used, provided thearea is solvent cleaned before and after blasting. For aluminum oraluminum alloys, chemical surface treatments are recommended, and suchtreatments may also be used for corrosion protection of parts subjectedto severe moisture environment. Such chemical surface treatments areeffected using any suitable method and material as well known in the artof surface treatment of aluminum including aluminum alloys. The materialof this invention should be applied within four hours of the completionof preparation, for avoidance of contamination or degradation. Thetreatment has been found effective for filling scores, grooves, andfretted areas of low-alloy steel, stainless steel and aluminum surfacessubject to sliding friction at temperatures between -40° F. and 400° F.Above 400° F. it is suitable for non-structural repairs.

The uncured material should be used carefully, preferably with gloves,and where skin has been exposed to it, the skin should be washedpromptly with soap and water.

The paste may be applied with a spatula and worked into the grooves andfretted areas sufficiently to displace any trapped air and to eliminateany voids from the filler material itself. Masking can reduce clean-uptime.

For spraying, the solvent is used to obtain a sprayable viscosity andthe surface sprayed. When deep areas are then filled, several layers aresprayed, letting the solvent evaporate between successive applications.After the completion of the spray applications, allow about one-halfhour at room temperature for solvent evaporation before curing.

During curing of either the paste or the sprayed material, no pressureis ordinarily required. Before cure, the adhesive mixture may be formedto its final contour.

Typical curing times are 31/2 hours at 250° F., 60 minutes at 300° F,and 25 minutes at 400° F. Curing may be done in an oven, and the part isusually allowed to oven-cool from its elevated temperature to near roomtemperature. Air cooling can be used where thermal expansion differencesare no problem. If the coefficients of thermal expansion are quitedifferent, it may be necessary to provide fixtures to hold the parts inposition during curing and cooling.

After cure, the part may be burnished or sanded, if needed.

EXAMPLE I

A paste comprising equal amounts by volume of molybdenum disulfidepowder (Molykote) and epoxy resin (Epon Adhesive 929) was applied 0.03inch thick to a metal surface. The area covered was cured for 1 hour at300° F, and then the material was subjected to a pressure test. Thiscomprised applying a pressure of 4 tons to a surface area 1/4 inch indiameter. The material continued to adhere to the metal surface in thisarea. This same application was given further tests. It was found thatthe casting stayed intact in Skydrol at 400° F. and that it remainedintact in air at temperatures over 600° F. Rockwell hardness testsshowed that the material was harder than mild steel.

Various aircraft parts were than covered with this same material, and itgave satisfactory use in practice.

EXAMPLE II

The formula of Example I was varied by using 90% by volume EA 929 and10% by volume molybdenum disulfide powder. The material still retainedits lubricating and hardness quality.

EXAMPLE III

One inch by 4inch by 0.062-inch thick coupons of 321 stainless steel,and 4130 steel were prepared. Surface preparation consisted of sprayingthe area to be bonded with Freon solvent and then wiping it off with apaper shop towel. A mixture of 50% by volume EA 929 adhesive (HysolDivision, Dexter Corporation) and 50% by volume molybdenum disulfidepowder by volume was prepared and was diluted with methylethylenechloride at a ratio of 3 parts methylethylene chloride to 1 part of themixture. The adhesive was then sprayed on both facing surfaces, and thespecimens were immediately assembled in one-half inch overlapconfiguration, 7.5-inches long and 1-inch wide. After 30 minutes at roomtemperature to enable evaporation of the methylethylene chloride, thespecimens were cured in an oven for 1 hour at 300° F.

After several weeks, the specimens were tested using the procedurespecified in ASTM D 1002 with a loading rate of 1200 psi per minute. For-40° F, 0° F, 250°F, 325° F, 365° F. and 400° F. testing, specimens werebrought to temperature and stabilized for 5 minutes before testing.Temperature was controlled by adhering a copper-constantin thermocoupleto the specimens which, when attached to a West Instruments Controller,automatically stabilized temperature at set-point. It usually took from10 to 20 minutes to bring the specimen to test temperature.

Four specimens each of the 321, and 4130 alloys were tested at -40° F.,80° F., 250° F., and either 365° F., or 400° F., depending on the alloy.Two specimens each were tested at 0° F. Failure strength was averagedand is shown in Table One. The drawing shows the average failure valuesversus temperature.

                                      TABLE ONE                                   __________________________________________________________________________    TENSILE SHEAR STRENGTH FROM                                                   -40°F. to + 400°F. OF SPECIMENS BONDED                          WITH THE MATERIAL OF THIS INVENTION                                                          MATERIAL/TEST RESULTS                                          PROPERTY/      321       4130                                                 TEMPERATURE    STAINLESS STEEL                                                                         STEEL                                                __________________________________________________________________________    1.                                                                              Tensile Shear Strength                                                        (psi) at 80° F.                                                      A.                                                                              Average      2398      2382                                                 B.                                                                              Average mean deviation                                                                     96        200                                                  C.                                                                              Individual test values                                                                     2280      2189                                                                2353      2270                                                                2417      2354                                                                2542      2714                                                 D.                                                                              Failure Mode 98% cohesive,                                                                           100% cohesive,                                                      porous from                                                                             voids in lap from                                                   trapped solvent                                                                         trapped solvent                                      2.                                                                              Tensile Shear Strength                                                        (psi) at 250° F.                                                     A.                                                                              Average      2300      2468                                                 B.                                                                              Average mean deviation                                                                     277       195                                                  C.                                                                              Individual test values                                                                     1894      2220                                                                2250      2345                                                                2396      2600                                                                2660      2708                                                 D.                                                                              Failure Mode 100% cohesive;                                                                          100% cohesive,                                                      holes in bond                                                                           porous from                                                         from trapped                                                                            trapped solvent                                                     solvent                                                        3.                                                                              Tensile Shear Strength                                                        (psi) at 400° F. for                                                   321,                                                                          and 365° F. for 4130                                                                400°F.                                                                           365° F.                                       A.                                                                              Average      1102      1067                                                 B.                                                                              Average mean deviation                                                                     263       314                                                  C.                                                                              Individual test values                                                                     729       1132                                                                1020      1549                                                                1213      1768                                                                1447                                                           D.                                                                              Failure Mode 95% cohesive                                                                            90% cohesive;                                                                 solvent trapped                                                               in lap-porous bond                                   4.                                                                              Tensile Shear Strength                                                        (psi) at 0° F.                                                       A.                                                                              Average      2601      2552                                                 B.                                                                              Average mean deviation                                                                     59        148                                                  C.                                                                              Individual test values                                                                     2542      2404                                                                2660      2700                                                 D.                                                                              Failure Mode 90% cohesive;                                                                           90% cohesive;                                                       porous from                                                                             porous in lap                                                       trapped solvent                                                                         from solvent                                         5.                                                                              Tensile Shear Strength                                                        (psi) at -40° F.                                                     A.                                                                              Average      2676      2260                                                 B.                                                                              Average mean deviation                                                                     181       336                                                  C.                                                                              Individual test values                                                                     2431      1690                                                                2583      2392                                                                2792      2396                                                                2895      2560                                                 D.                                                                              Failure Mode 90% cohesive;                                                                           90% cohesive;                                                       porous from                                                                             bond porous from                                                    trapped solvent                                                                         trapped solvent                                      __________________________________________________________________________     NOTES.                                                                        Cohesive Failure indicates failure within the adhesive, as distinct from      failure of the adhesive bond to the metal surface.                       

Test results indicate that bond strengths of 321 stainless steel and4130 steel are similar. It should be noted that the surfaces to bebonded were very rough, hence a high degree of mechanical adhesion wasobtained. Smooth steel surfaces should be solvent wiped, vapor honed orgrit blasted and then recleaned with solvent before bonding for optimumadhesion. Since bondline failures of the steel specimens were basicallycohesive, these tests appear to measure the "adhesive-ness" of thefiller mixture.

While the test results shown in the drawing were below the strength ofthe unfilled EA 929 adhesive, since the molybdenum disulfide powder hasa plasticizing effect on the EA 929 adhesive, the strength of themixture is adequate for surface filling applications. The trends of thetensile shear versus temperature graphs indicate that, above 500° F.,little adhesive strength can be expected. The data sheet for EA 929 alsoindicates excellent load bearing at 300° F. but erratic performanceabove 400° F. The mixture of this invention presents a relatively hardwear surface and appeared to elongate very little before failure.

The mixture of EA 929/molybdenum disulfide has a high degree ofelectrical resistivity. When measured with a Simpson VOM on the mostsensitive resistance scale, no needle deflection was noted.

All failed specimens showed some degree of solvent entrapment duringcure of the adhesive. This was evidenced by porosity, voids and "worm"holes in the adhesive/surface interface. This indicates that themixtures should be deposited in layers so as to evaporate the trappedsolvent before depositing the next layer of the surface filler.

Tensile shear strength of statically tested 321 and 4130 steelspecimens, bonded with a "by-volume" mixture of 50% EA 929 adhesive and50% molybdenum disulfide powder, appears more than adequate for surfacefilling applications over the temperature range -40°F. to +400°F.Solvent wipe surface preparation is effective if the adherends alreadyhave a rough surface. Grit blasting, vapor honing or chemical etchingare recommended as prebonding preparation for smooth surfaces.

EXAMPLE IV

A steel pneumatic cylinder had a 3 inch, 120° circumferential groovefilled to a depth of 0.020 to 0.030 inch by the method described inExample I above. This unit, was given approximately 300 hours ofservice, and the repaired unit still looked good.

EXAMPLE V

A high-pressure modulating shutoff valve honing a steel surface wasrepaired. Two longitudinal grooves were filled and honed in a 3 inchlength, one-half inch width area. Some small surface pits were noted,but the repair looked fairly good after an estimated 2907 hours ofservice.

To those skilled in the art to which this invention relates, manychanges in construction and widely differing embodiments andapplications of the invention will suggest themselves without departingfrom the spirit and scope of the invention. The disclosures and thedescription herein are purely illustrative and are not intended to be inany sense limiting.

We claim:
 1. A repair process for restoring damaged metal, carbon, orother original surfaces by filling score marks, grooves, and otherirregularities in the surface of articles such as pneumatic andhydraulic cylinders without changing the basic dimensions of sucharticles comprising:filling all scores, grooves, and surfaceirregularities of said surface with a mixture of finely powderedmolybdenum disulfide and epoxy resin adhesive, wiping the filledsurfaces to remove any excess mixture where it extends significantlyabove the original surface level, and curing said resin at a temperaturewell above ambient for a time sufficient to complete the cure thereofand provide a material hard as mild steel and resistant to hydraulicfluids, said mixture consisting essentially of from 10% to 90% by volumeof said disulfide of particle size no larger than 60 microns and from90% to 10% by volume of said resin adhesive, said adhesive being aglycidyl polyether of bisphenol-A containing a curing agent and having aBrookfield viscosity of 400,000 cps at 75°F.
 2. The process of claim 1wherein said filling step includes first thinning said mixture with avolatile solvent to a viscosity sufficient for spraying and thenspraying the thinned mixture on said surface and into all scores,grooves, and surface irregularities thereof, and evaporating saidsolvent before said wiping step.
 3. The process of claim 1 wherein saidcuring step is followed by abrading off surplus cured coating to leavethe original surface uncoated except where there were said scores,grooves or surface irregularities.
 4. The process of claim 1 whereinsaid surface is steel or stainless steel.
 5. The process of claim 1wherein said mixture consists essentially of from 60% to 40% by volumeof said molybdenum disulfide and from 40% to 60% by volume of saidadhesive.
 6. The process of claim 1 wherein said mixture consistsessentially of equal volumes of said molybdenum disulfide and saidadhesive.